Color photographic elements are conventionally formed with superimposed blue, green, and red recording layer units coated on a support. The blue, green, and red recording layer units contain radiation-sensitive silver halide emulsions that form a latent image in response to blue, green, and red light, respectively. Additionally, the blue recording layer unit contains a yellow dye-forming coupler, the green recording layer unit contains a magenta dye-forming coupler, and the red recording layer unit contains a cyan dye-forming coupler.
Following imagewise exposure, a negative working photographic element is processed in a color developer that contains a color developing agent that is oxidized while selectively reducing to silver the latent image bearing silver halide grains. The oxidized color developing agent then reacts with the dye-forming coupler in the vicinity of the developed grains to produce an image dye. Yellow (blue-absorbing), magenta (green-absorbing) and cyan (red-absorbing) image dyes are formed in the blue, green, and red recording layer units, respectively. Subsequently the element is bleached (i.e., developed silver is converted back to silver halide) to eliminate neutral density attributable to developed silver and then fixed (i.e., silver halide is removed) to provide stability during subsequent room light handling.
When processing is conducted as noted above, negative dye images are produced. To produce corresponding positive dye images, and hence, to produce a visual approximation of the hues of the subject photographed, white light is typically passed through the color negative image to expose a second color photographic material having blue, green, and red recording layer units as described above, usually coated on a white reflective support. The second element is commonly referred to as a color print element. Processing of the color print element as described above produces a viewable positive image that approximates that of the subject originally photographed.
A positive working color photographic element is first developed in a black-and-white developer where the exposed crystals are selectively reduced to metallic silver. The unexposed silver is then fogged and reduced by a chromogenic color developer in a subsequent step to generate cyan, magenta, and yellow image dyes. The film is further bleached and fixed as with the negative working film. The positive working film thus forms dyes in the unexposed areas and renders a positive image of the scene, directly.
A problem with the accuracy of color reproduction delayed the commercial introduction of color negative elements. In color negative imaging, two dye image-forming coupler containing elements, a camera speed image capture and storage element and an image display, i.e. print element, are sequentially exposed and processed to arrive at a viewable positive image. Since the color negative element cascades its color errors forward to the color print element, the cumulative error in the final print is unacceptably large, absent some form of color correction. Even in color reversal materials which employ just one set of image dyes, color correction for the unwanted absorption of the imperfect image dyes is required to produce acceptable image color fidelity for direct viewing.
Color correction means, for color negative or color reversal elements, have relied on imagewise interlayer development modification effects during wet chemical processing called interlayer interimage effects. In the case of color negative elements, these effects are most commonly achieved with development inhibitor releasing (DIR) couplers that imagewise release development inhibitors to reduced the extent of development of the receiving silver halide grains, and with colored masking couplers. In the case of color reversal elements, these effects are usually achieved through imagewise interlayer silver halide emulsion development inhibition during the first black-and-white development, and possibly with DIR couplers during the second color development step.
Alternatively, instead of optical print-through exposure to create a color print, the color negative or color reversal element can be scanned to record the blue, green, and red densities in each picture element (pixel) of the exposed area. The color correction that is normally achieved by chemical interlayer interimage effects can be achieved by electronically manipulating stored image information as its image-bearing signal. One example of electronic color correction produced by scanning a processed photographic recording material and manipulating the resultant image-bearing electronic signals to achieve improved color rendition can be found in the KODAK Photo CD.TM. Imaging Workstation system. In addition, optical printing by passing light through the processed photographic recording material to expose a second light-sensitive material is no longer necessary. The light exposures necessary to write the color-corrected output onto a suitable display material such as silver halide color paper exposed by red, green, and blue light emitting lasers can be calculated and those device-dependent writing instructions can be transmitted to such alternate printers as their code values (specific instructions for producing the correct color hue and image dye amount). Other means of electronic printing include thermal dye transfer material, color electrophotographic media, or a three color cathode ray tube monitor.
It has been found unexpectedly that different or larger color corrections can be managed by electronic color correction than can be achieved through chemical interlayer interimage effects in color negative or color reversal films. This enhanced capability allows the possibility of producing better colorimetric matches between the original scene color content and the rendered image reproduction. In order to accomplish improved color reproduction, more accurate photographic recording material spectral sensitivity is required. In particular, the spectral sensitivity of a film optimally designed for scanning and electronic color correction must more closely approach that of the human visual system. To accurately record colors the way the human eye perceives them, a recording element must have spectral sensitivities that are linear transformations of the blue, green, and red cone responses of the human eye. Such linear transformations are known as color matching functions. Color matching functions for any set of real primary stimuli must have negative portions. Within the realm of known photographic mechanisms, it is not possible to produce a photographic element having spectral sensitivities whose response is negative.
Examples of spectral sensitivities that approximate color matching functions are those of MacAdam (Pearson and Yule, J. Color Appearance, 2, 30 (1973). Giorgianni et al, U.S. Pat. No. 5,582,961 and U.S. Pat. No. 5,609,978, the disclosures of which are herein incorporated by reference, describe related spectral sensitivities applied to non-tabular emulsions in color reversal film elements capable of forming image representations that correspond more closely to the colorimetric values of the original scene upon scanning and electronic conversion. A characteristic of these color matching functions is a broad response for the blue component that has significant sensitivity at wavelengths beyond 480 nm. This type of response function closely resembles the blue response of the human eye and visual system.
The blue sensitivity of a multilayer film element is determined by the light absorption profile of the silver halide emulsions in the blue sensitive layer unit attenuated by any ultraviolet light absorbing materials that lie above it in the top layers of the film, such as ultraviolet filter dyes, Lippmann emulsions, and polymeric beads used to reduce friction in the top layers of the film. The light absorption of the emulsions used in the blue sensitive layer unit is in turn determined by the composite absorption of the specific combination of spectral sensitizing dyes adsorbed to the surface of the silver halide crystals and the intrinsic blue light absorption of silver bromide and silver iodide. Blue sensitive emulsions commonly found in the art are observed to employ a single blue sensitizing dye, and rely largely on the native (intrinsic) blue light sensitivity of silver iodobromide for speed. Broad light absorptance to produce color reproduction accuracy in accord with human visual sensitivity was not sought.
Kam Ng et al U.S. Pat. No. 5,460,928 discloses a tabular silver iodobromide emulsion dyed with two J-aggregating cyanine dyes to produce improved illuminant sensitivity, but insufficient bathochromic spectral absorptance and overall half-peak dyed absorptance bandwidth is provided by the dyed emulsion. Giorgianni et al '961 and '978 likewise demonstrate a conventional, low aspect ratio silver iodobromide emulsion dyed with two J-aggregating cyanine dyes, but again insufficient bathochromic spectral absorptance and overall half-peak dyed absorptance bandwidth is provided by the dyed emulsion disclosed. Their goal of significantly broad blue sensitivity to overlap with the green sensitivity to mimic the human visual system was not fully satisfied.
In order to achieve accurate color reproduction, the photographic element blue sensitivity must meet certain requirements provided by dyed silver halide emulsions. The emulsions' material properties include the correct wavelength of maximum spectral absorptance and the requisite bandwidth of absorption to confer the correct spectral responsivity to high-latitude photographic recording materials. A need for the efficient blue light spectral sensitization of silver halide emulsions remains.